1. Field of the Invention
The present invention relates to a plasma ignition device for an internal combustion engine, and more particularly, to output abnormality detection in a power supply circuit.
2. Description of the Related Art
Up to now, in a power supply circuit for an internal combustion engine ignition device, a tank capacitor connected in parallel to an ignition plug is charged by a booster circuit, and a voltage detector circuit outputs a given signal upon detecting that a charging voltage of the tank capacitor reaches a given voltage. The operation of the booster circuit stops in response to that signal to stabilize the charging voltage of the tank capacitor (for example, refer to JP 05-231281 A).
However, in the case where a center electrode is grounded by a current leakage from an ignition plug connected to an output unit, or the like, resulting in the occurrence of an output abnormality (hereinafter, referred to as “at the time of ground”), a charging voltage of the tank capacitor does not reach the given voltage, and the voltage detector circuit does not output the given signal. For that reason, the booster circuit continues to operate, thereby causing such a problem that electronic parts such as a transformer or a field effect transistor (FET) of the booster circuit are broken down.
Further, when a request output of an ignition coil is increased by the ignition plug covered with gasoline or the like to cause an accidental fire, and an abnormal output occurs (hereinafter, referred to as “at the time of accidental fire”), an output voltage of the ignition coil is applied between the tank capacitor and the ignition plug in a backward direction of a high-voltage diode inserted in a direction from the tank capacitor to the ignition plug as a forward direction, thereby resulting in a risk that the high-voltage diode is broken down.